A. Field of the Invention
This invention relates to a well safety valve system comprising a tubing retrievable valve coupled with a safety valve landing nipple which utilize a dual pressure fluid system and which is capable of having at least the balance line flushed into the well bore.
B. The Prior Art
In subsea production from a well it is desirable to have safety valve means for shuting off the flow from the well in the event of emergency or other event requiring cessation of flow. It is common to incorporate a safety valve in such well, such as a remote-controlled tubing retrievable safety valve. That is, the valve is made up in the well tubing string. Valves suitable for such purpose are illustrated and described at pages 4002 and 4003 of The Composite Catalog of Oilfield Equipment and Services, 1974-75 Edition, published by World Oil, Houston, Tex.
Due to the complexity and cost of pulling the tubing string in order to replace a tubing retrievable safety valve (TRSV), in the event of failure, a great effort has been made to provide a method for installing a secondary safety valve within the tubing string, usually within the TRSV itself. This is accomplished by having a tool landing profile inside the bore of the TRSV.
Remote controlled safety valve landing nipples which can be made up in a tubing string are well known in the art. Such landing nipples are illustrated on page 4,004 of The Composite Catalog of Oilfield Equipment and Services, 1974-75 Edition, World Oil, Houston, Tex. Such landing nipples are usually included in the tubing string when it is planned to use either through the flow line (TFL) or wire line placement of safety valves.